Re: [PATCH v2] io_uring/rsrc: fix RLIMIT_MEMLOCK bypass by removing cross-buffer accounting

Jens Axboe
2026-01-19T23:40:16Z

On 1/19/26 4:34 PM, Yuhao Jiang wrote:
> On Mon, Jan 19, 2026 at 11:03 AM Jens Axboe <axboe@kernel.dk> wrote:
>>
>> On 1/19/26 12:10 AM, Yuhao Jiang wrote:
>>> The trade-off is that memory accounting may be overestimated when
>>> multiple buffers share compound pages, but this is safe and prevents
>>> the security issue.
>>
>> I'd be worried that this would break existing setups. We obviously need
>> to get the unmap accounting correct, but in terms of practicality, any
>> user of registered buffers will have had to bump distro limits manually
>> anyway, and in that case it's usually just set very high. Otherwise
>> there's very little you can do with it.
>>
>> How about something else entirely - just track the accounted pages on
>> the side. If we ref those, then we can ensure that if a huge page is
>> accounted, it's only unaccounted when all existing "users" of it have
>> gone away. That means if you drop parts of it, it'll remain accounted.
>>
>> Something totally untested like the below... Yes it's not a trivial
>> amount of code, but it is actually fairly trivial code.
>
> Thanks, this approach makes sense. I'll send a v3 based on this.

Great, thanks! I think the key is tracking this on the side, and then
a ref to tell when it's safe to unaccount it. The rest is just
implementation details.

--
Jens Axboe